1. Field of the Invention
This invention relates to a high speed seal for a rock bit.
More particularly, this invention relates to a high speed metal-to-metal seal for a rock bit that initially provides a resilient rubberlike O-ring seal during the early running of the bit and, as the seal wears, the seal becomes a metal-to-metal seal as the bit continues to run in a borehole.
2. Description of the Prior Art
There are many prior art patents that describe composite seals that are made up of resilient material that encapsulates or is adjacent to a metal sealing ring or the like. For example, U.S. Pat. No. 3,381,968, assigned to the same assignee as the present invention, describes and teaches one or more belleville type of rings encapsulated within a resilient sealing material with mating surfaces that contact both the leg of a rock bit surrounding a journal pin and a cone mounted on the journal pin. The belleville spring provides a means to accommodate for irregularities associated with the cone rotating on the journal pin. There is no metal-to-metal sealing contact as taught in the present invention.
The present invention initially serves as an ordinary O-ring and progresses towards a metal-to-metal seal as the half-round rubberized portion wears off, allowing the metal portion of the seal to gradually seat into the bearing surface of the opposing cone or leg portion of a rock bit.
U.S. Pat. No. 3,761,145 describes a metal-to-metal seal with an oval-shaped O-ring positioned adjacent a metal sealing ring. The O-ring serves to urge the sealing ring into metal-to-metal contact with an adjacent cone of a rock bit. A portion of the journal supporting the cone nearest the bearing surface is conical in shape, thus biasing the oval-shaped O-ring against the metal-to-metal sealing ring. The O-ring forces the sealing surface of the ring into contact with the bearing surface of the cone. This patent is disadvantaged in that the metal-to-metal seal must be lapped-in before the rock bit is operational. Otherwise lubricant from within the bearing surfaces can escape by the sealing surface before the metal-to-metal surfaces are adequately seated. Once lubricant escapes from the bearing surfaces of a rock bit, the operating life of the rock bit is considerably shortened in that the bearings easily become overheated and will fail due to lack of lubricant in the bearing.
The present invention substantially eliminates any tendency to lose lubricating grease from within a roller cone. Upon initial actuation or operation of the bit the seal acts as an ordinary resilient O-ring and, as the cone continues to rotate on its journal, the protruding rubber portion of the seal adjacent the bearing surface of the cone wears away, gradually allowing the metal sealing face of the seal to lap into sealing engagement with adjacent sealing surfaces on a cone or a journal of a rock bit. Thus little or no lubricant can escape past the seal due to the fact that the rubber portion of the seal prevents this from happening.